I would suggest just saving your money for the Socket 939 rig. You should wait for 1-3 months after the new AMD socket is released to get the Socket 939, cause there will likely be a sharp decline in the price of Socket 939 hardware.
So far, I haven't seen any comments on WHY you want to upgrade... OK, you don't like AGP 4x, and you can't overclock.... that hardly sounds like a reason to upgrade though...
Do you play games with this rig?
- looking for faster frame rates?
- higher resolutions?
You get the point.... Try to give a better idea of WHAT you're trying to accomplish, or what your computer is DOING that you don't like.